This invention relates to camera shutter mechanisms, and more particularly, to a shutter mechanism for differentially varying the film exposure over a film frame.
In photographing a scene having large variations in spatial brightness, and particularly where exposure is carried out under the control of a photocell, it is not unusual for details in the brightest regions to be washed out by over-exposure and for details in the darkest region to be concealed by under-exposure of the photosensitive material on the film frame. For a given scene, the extent of the problem depends on the characteristic curve, (i.e., the density-log exposure curve) of the photosensitive material being used. Where the brightness range in the scene being photographed and the photosensitive film material are such that many details are lost by reason of the exposure being determined by the average scene brightness, improved results can be achieved, for some scenes, by controlling exposure in accordance with a spatially weighted average of scene brightness. Thus, it is conventional to weight the photocell viewing angle to reduce the response to light from the upper portion of a scene, which usually will be the sky during daylight, outdoor photography so that the photosensitive element will be more responsive to the central portion of the scene where a person's face, for example, is located in the usual photographic setting. In such case, the central region, where it is desired for the detail to be the most distinct, will dominate the photocell's response and will result in a more pleasing photograph at the expense of some regional over- or under-exposure in peripheral portions of the photograph. The photocell response can be modified by optics associated with the photocell. Alternatively, the response can be electronically modified such as shown in U.S. Pat. No. 3,409,378. Regardless of the technique utilized, however, any improved result will depend on whether the actual scene being photographed corresponds to the design criteria built into the photocell response.
Significant improvement in the photographic image has been achieved by focal plane shutters having a modulated aperture width for differentially exposing individual regions of a film frame in accordance with the brightness of the regions in the scene being photographed. U.S. Pat. No. 3,116,670, which is typical of the above-noted shutter mechanism, discloses a focal plane shutter having means for controlling aperture width to modulate the light reaching the photosensitive material during the transit thereover of the shutter curtain. Such means includes a photocell positioned to receive light passing through the camera lens and reflected from a narrow strip at the leading edge of the curtain slot, and an electromagnet for modulating the width of the slot in accordance with the output of the photocell. Thus, the exposure of elemental strips of the photosensitive material is modulated in accordance with the average brightness of the scene within the strip. Other examples of variable focal plane shutters are described in U.S. Pat. Nos. 3,479,936 and 3,442,198.
While the above noted shutter mechanisms may give improved results in scenes where the brightness gradient runs in the same direction as the direction of movement of the shutter, it cannot provide significant improvement when the brightness gradient in all or a part of the scene is parallel to the slot of the shutter curtain. Furthermore, by reason of the time required for a focal plane shutter to complete its traverse of a film frame, this approach is not suitable for a hand-held camera where maximum exposure time should not exceed about 1/30 of a second to prevent blurring due to reflex movements on the part of the photographer.
It is therefore an object of the present invention to provide a new and improved shutter mechanism of the type described which overcomes or substantially reduces the above-described limitations of conventional shutter mechanisms of the type described.
According to the present invention, there is provided a camera having a segmented shutter mechanism, the latter comprising a plurality of shutter elements, each of which is associated with a predetermined elemental area of the film frame, and each of which is selectively operable independently of the other elements for transmitting light from a given area of the scene being photographed to the elemental area with which the shutter element is associated; and means associated with each shutter element for independently operating the same responsive to the brightness of the different areas of the scene.
The plurality of shutter elements can be arranged in a two-dimensional array with respect to the film frame permitting each elemental area thereof to be exposed in an optimum manner independently of any other area. Thus, a shutter mechanism according to the present invention can enhance the recorded image regardless of the location or direction of brightness gradients in the scene being photographed. More specifically, it advantageously controls the exposure value of each elemental film area of the film by varying the time of exposure for each such area.
In the preferred arrangement, actuation of the shutter mechanism to initiate exposure causes simultaneous unblocking operation of each shutter element for effecting transmission of light from the scene to the film frame. When a total predetermined amount of light is transmitted by each shutter element, the operating means associated with each shutter element terminates operation thereof; interrupting transmission of light and terminating exposure of the elemental area with which the shutter element is associated. Thus, exposure of the elemental areas takes place in parallel; and the maximum time required for the shutter mechanism to effect exposure is no longer than the time required to properly expose the darkest elemental area of the scene being photographed. This can be limited to a maximum time consistent with a hand-held camera.